1. Field of the Invention
This invention relates to a method and apparatus for patterning a substrate and more particularly relates to a method and apparatus for separating a stamper from a patterned substrate.
2. Description of the Related Art
Nanoimprint technology has developed rapidly in the past decade and offers promising advancements with regards to the replication of nanometer-scaled structures. The technological improvements have been a boon to several growing industries including integrated circuits (IC), micro electro mechanical systems (MEMS), and magnetic storage mediums. Replicating minute structures, however, introduces several problems that must be surmounted in order to refine the imprinting process. Forces such as friction and adhesion, for example, must be overcome in order to achieve optimal results. In addition, inexpensive mechanisms and simplistic methods are needed to advance the imprinting process and to make the process more cost effective.
Imprint (or “nanoimprint”) lithography has been proposed as an effective method to generate patterned magnetic media for use in storage devices. Imprint lithography is a method of lithography that uses a mold (stamper) or a mechanical force to pattern a resist. In certain embodiments, a formed pattern is created on a surface of the stamper using electron beam (e-beam) lithography, enabling the formation of high resolution features on the stamper. E-beam lithography is a relatively expensive and prolonged process, however, often requiring months to complete a pattern. The finished stamper, though, may be used repeatedly in a relatively inexpensive process to transfer the e-beam formed pattern onto a substrate surface.
FIGS. 1A-1F depict a series of cross-sectional views illustrating a substrate 100 subjected to a prior art imprint lithography process to create nano-scaled features, such as pillars 108 for creating data recording bits. The substrate 100 includes a resist layer 102 (FIG. 1A). The resist layer 102 is shaped by a stamper 104 and cured to create pillars 106 in the resist (FIG. 1B-1C). The resist layer 102 functions as a mask (FIG. 1D) to resist ions 114 during a reactive ion etching (RIE) process. Pillars 108 are etched into the substrate 100 (FIG. 1E). A magnetic layer 110 is subsequently deposited over the pillars 108 (FIG. 1F) to provide magnetic islands for data recording bits, thereby forming the foundation for patterned magnetic media.
Imprint lithography processes generally require that the resist be cured either by ultra violet (UV) light or by thermal energy. In thermal imprinting, the stamper 104, the sample substrate 100, or both are heated to soften the resist 102 during the imprinting process. Upon cooling, the imprinted resist patterns or features 106 solidify, retaining the imprinted shape after removal of the stamper 104.
In UV-cure imprinting, a transparent stamper 104 is pressed against a substrate 100 coated with a liquid photopolymer resist 102. After exposure to UV light 112 (FIG. 1B), photo initiators in the resist cause the resist 102 to polymerize into a solid, leaving solidified topographic features 106 in the cured resist layer 102 (FIG. 1C). Pressure may be applied to the stamper 104 and/or substrate 100 during the curing process to ensure complete formation of quality features 106 in the resist 102.
In the depicted embodiment, the stamper 104 comprises minute holes 116, which may be patterned to correspond to data recording bits of patterned magnetic media. Patterned media can provide increased bit density and storage capacity with greater thermal stability than conventional multigrain magnetic media. Patterned media can be formed by a variety of methods known to those skilled in the art in addition to the depicted imprint lithography process.
To form patterned media, a highly ordered array of pillars 108, or magnetic islands, is typically formed on the substrate 100 surface. High density is achieved by storing data in tracks just one island wide, rather than tracks wide enough to accommodate multiple (typically on the order of 10) random grains. In one embodiment, the pillars 108 or holes 116 are approximately 20 nm in diameter. Viable data storage densities of around one terabits per square inch may be achievable with patterned media.
Once the features 106 in the resist layer 102 are formed, the stamper 104 must be separated and removed from the substrate 100. Because the holes 116 in the stamper 104 increase the effective surface area of the stamper 104, the surface energy generally causes the stamper 104 to stick to the resist layer 102, requiring a substantial force to decouple the stamper 104 from the substrate 100. Typically, a pin, hook, wedge, or other mechanical device may be used to force the separation.
Directly lifting the stamper 104 requires a large force to achieve separation that may cause mechanical damage to the imprinted features. Direct contact with the substrate 100 surface and/or the stamper 104 surface is generally undesirable because contact can also damage the miniscule features and impair any potential functions, such as data throughput, for example. Furthermore, using a chisel or wedge to propagate a Mode 1 crack from the outside diameter of a disk or the like may reduce the amount of force required for separation, but can also introduce unbalanced forces causing non-uniform separation. To initiate a uniform separation, multiple wedges functioning simultaneously, mechanical tilting, or other mechanical feats that are difficult to achieve may be required.
From the foregoing discussion, it should be apparent that a need exists for a method and apparatus that facilitate separation of the stamper from the substrate. Beneficially, such an apparatus and method would provide a simple force to uniformly separate the stamper from the substrate without causing harm to either the substrate or the imprinted features. In addition, the method and apparatus would be inexpensive, easy to implement and executable in a minimal amount of time.